A biodiversity inventory of the freshwater snail fauna of Holmes Creek, Florida

1. Introduction

The freshwater snail
fauna of Holmes Creek is of particular interest because of the richness
of the fauna and the abundance of most species found there. The report
is based on biodiversity inventories conducted by the author. All
species records are based on specimens deposited in the Florida Museum
of Natural History. Museum catalogue numbers are cited in column 3 of
Table 2. For purposes of this report they are regarded as voucher
specimens. In the absence of voucher specimens claims of species
identifications could be considered hearsay.

Biodiversity surveys
were
conducted with the objective of obtaining specimens of all snail
species present at a particular locality using standard qualitative
survey techniques. The success of each survey was influenced by water
levels at the time of the visit. High water levels constitute difficult
survey conditions. Low water levels constitute optimal survey
conditions. Water-level conditions explain, in part, different results
between two or more site-visits at a given locality. Twenty-two (22)
species of freshwater snails (TABLE 1) were found in Holmes Creek
during forty-one (41) site-visits (FGT...., Column 2, Table 2) at
thirty-one (31) field stations in surveys conducted between May 1970
and June 2000 (TABLE 2). Freshwater bivalves (clams) of the genera Pisidium
and Corbicula are included in the TABLE 2, but are given no
further accord.

Holmes Creek begins
as a small slough-like stream in southern Alabama. It enters Florida
near Graceville, and flows southwest to enter the Choctawhatchee River
west of Ebro, Florida. During the first half of its course Holmes Creek
has the characteristics of a slough-like stream. It is narrow and
shallow. There is a slight current. The creek flows over a sand-silt
substrate, and the water is acid-brown and has a relatively low mineral
content with a pH > 7.0. The faunal diversity through this
section of the creek is relatively small, and it includes species that
are also found in the lower section of Holmes Creek as well as in other
river systems. Species found in this section of the creek are listed
under Site-visits1-8 in TABLE 2.

In Washington
County, about one mile downstream from the Hwy 276-A bridge, Holmes
Creek receives discharge from a midstream spring-source known locally
as Burn-out Spring (30°40.9' N, 85°38.8' W). This is the first
significant spring along Holmes Creek. From this point downstream the
creek flows over exposed limestone bedrock, and it receives discharge
from numerous seeps and small springs, as well as from some first and
second magnitude springs. From Burn-out Spring downstream to the
Choctawhatchee River Holmes Creek becomes progressively clearer, it
acquires a higher mineral content, it rapidly increases in water-flow
volume, and it's molluscan biodiversity increases. Species encountered
in this section of Holmes Creek are recorded under site-visits 9-41 in
TABLE 2.

2. Geographic significance of the Holmes Creek freshwater
snail fauna

Fifteen species are widely distributed, and their presence in Holmes Creek has no
particular biogeographic significance. These species are:

Pomacea paludosa

Campeloma geniculum

Elimia curvicostata

Somatogyrus walkerianus

Notogillia wetherbyi

Pseudosuccinea columella

Fossaria modicella

Physella gyrina

Physella hendersoni

Physella cubensis

Planorbella trivolvis

Gyraulus parvus

Micromenetus dilatatus

Laevapexsp.

Ferrissia sp.

One species is found
only in the Choctawhatchee River - Holmes Creek - Chipola River
drainage systems. This species is:

Elimia dickinsoni

Three species are
found only in Holmes Creek and the Chipola River drainage systems.
These species are:

Lioplax pilsbryi

Viviparus goodrichi

Rhapinema dacryon

Three species are
endemic to the Holmes Creek drainage system. All are unnamed. They are:

Elimia n. sp.

Spilochlamys n. sp.

Lyogyrus n. sp.

Elimia n. sp.
is widely distributed in Holmes Creek. It is the commonest large-sized
species of snail in the creek. It had been recorded earlier as Elimia
clenchi, a species endemic to, but widely distributed and abundant
in, the Choctawhatchee River. Early growth stages of the two species
are similar, which explains the confusion in some earlier
identifications.

Spilochlamys
n. sp. is confined principally to the lower section of Holmes Creek in
springs and in clear spring fed waters. It is most closely related to Spilochlamys
conica Thompson, 1968, which is found in the Flint
River system south east to the Withlacoochee River system.

Lyogyrus n.
sp. is known only from three springs along the middle section of Holmes
Creek. It is restricted to cool, clear pristine water. It is most
closely related to Lyogyrus latus Thompson and
Hershler, 1991, which is found in the Flint River system and the
Ocmulgee River system in Georgia. It is the species in Holmes Creek
most susceptible to adverse environmental disturbances upstream of its
distribution. Factors that could influence its survival in Hightower
Spring and in the "unnamed spring" (Site-visits 26, 27)

Three species found
in the Choctawhatchee River were not found in Holmes Creek:

Elimia clenchi (Goodrich, 1924)

Elimia n. sp. #2

Somatogyrus n. sp.

3. Conservation of the Holmes Creek freshwater snail fauna

The freshwater
snail fauna of Holmes Creek is remarkable for its rich diversity of
species. It is the richest freshwater fauna in the Florida panhandle,
including the Choctawhatchee River and all of it's other tributaries.
It is the second most diverse freshwater fauna in Florida. The St.
John's River system has a more diverse fauna, but is drains a much
larger geographic area. At present the fauna in Holmes Creek appears to
be in pristine condition. No apparent changes in species composition or
distributions were detected over a thirty-year sampling period. No
municipalities lie along Holmes Creek, except for Graceville and
Vernon. Both of these town are small, and sewage contamination and
street run-off are minimal. Resident septic tank contamination along
the creek is also minimal, with one or two possible exception. Water
drawdown for agricultural purposes appears not to have an effect on the
fauna currently.

Maintaining Holmes
Creek in its present condition should be a priority for water resource
management, land use management and biodiversity conservation. The
species that are most susceptible to extinction are those species
endemic to the creek. A single major adverse environmental event in the
creek could cause the extinction of Lyogyrus n. sp., Spilochlamys
n. sp. and Elimia n. sp., in that order. These three species
are confined to the creek, they have no out-lying populations, and
their limited mobility would prevent them from avoiding adverse change.
Other species also could be extirpated from Holmes Creek by such an
event, but they would still survive in other stream systems where they
currently exist.